The vast majority of engines in cars and trucks on the road today are internal combustion engines that employ a cam to open and close the inlet and exhaust valves of the engine. It is well known in the art of internal combustion engine design that whenever maximum power output at high RPM is desired, a high lift, rapid opening and closing cam profile is necessary, combined with a long overlap timing for the inlet and exhaust valves.
Conversely, when fuel economy and low emissions are the main concern then a very different cam profile is required having little lift, slow opening and closing and almost no overlap timing.
Most engines in everyday road use rely on a compromise valve timing that is the result of a fixed cam profile being used to cover the whole engine speed range. The results are moderate fuel economy, moderate emissions and moderate power output.
Prior art in the design of variable valve timing mechanisms have attempted to overcome the deficiencies of pre-set valve timing.
U.S. Pat. No. 4,942,853 to Konno and U.S. Pat. No. 4,726,332 to Nishimura disclose valve operating systems that employs a combination of low and high speed cam profiles that are engageable with sets of independent rocker arms through the operation of hydraulically actuated pins and dog clutches to vary the operation of the valves at specified engine speeds.
U.S. Pat. No. 4,887,562 to Wakeman discloses a self-contained hydraulic valve timing system that operates within a specially designed cylinder head. The hydraulic system is used to operate a solenoid valve to establish a lock between the cam and valve stem.
Further examples of variable valve mechanisms known to applicant include:
U.S. Pat. No. 4,708,101 to Hara PA1 U.S. Pat. No. 4,475,489 to Honda PA1 U.S. Pat. No. 4,502,426 to Skelley PA1 U.S. Pat. No. 3,413,965 to Gavasso PA1 a first cam engaging arm mountable on said rocker shaft for pivotal movement about said shaft; PA1 a second valve lifter engaging arm mountable on said rocker shaft for pivotal movement about said shaft; PA1 said arms sharing a common pivoting axis when mounted on said rocker shaft; PA1 coupling means interposed between said first and second arms to adjust the relative pivotal positions of said arms with respect to each other on said rocker shaft in order to vary the overall rocker arm shape and to releasably lock said first and second arms together for movement as a single unit when following said cam.